WEST LAFAYETTE, INDIANA - There are more than 900 species of ticks in the world, many of which carry serious diseases. In fact, ticks transmit a wider variety of pathogens than any other arthropod, causing thousands of human and animal deaths annually. But no one had thought to study them until about 10 years ago.
Now researchers, led by Purdue University entomologist Catherine Hill, have mapped the genome of Ixodes scapularis, the deer tick that is infamous for carrying Lyme Disease. With backing from the National Institutes of Health, Hill put together a tick research team of 93 scientists from 46 institutions around the world. Their findings are published in Nature Communications.
"A good way to think about a genome-sequencing project is to relate it to a jigsaw puzzle," Hill explained. "So you break everything up like little pieces of DNA and then you have to put them back together again."
Among other things, the researchers identified a long list of genes that control smell and taste receptors, and discovered that ticks smell with their feet. The creatures climb blades of grass and hold their feet out until they sense a host to hop onto. With that information, scientists can design sprays and repellents to disrupt the tick’s abilities to find a host or perhaps even to mate and propagate.
Targeted pesticides and medicines
The researchers also determined that about 20 percent of the creature's genes are unique to ticks, which Hill says could lead to highly focused pesticides.
"If we target these particular molecules we can make designer chemistries that are very specific or unique to the tick. We would be controlling only the tick and not affecting other organisms in the environment," she said. "And that means that we would be aiming to design more environmentally acceptable products for tick control."
Hill’s colleague, virologist Richard Kuhn, heads Purdue's Institute for Inflammation, Immunology and Infectious Diseases. He sees the tick genome map as a gateway for the development of new drugs, noting that although ticks and humans use the same biological approach to disable viruses, ticks have developed immunity to many of the pathogens they carry.
Kuhn suggests scientists could apply the same principles to human medicine. Knowledge of the Ixodes scapularis genome will not only help scientists develop vaccines for Lyme disease, anaplasmosis, and a form of encephalitis, it could also prevent future tick-related epidemics.
Preparing for the spread of ticks
Diseases spread by ticks are on the rise around the world, spurred by a combination of factors, including shifting climates and population sprawl into rural areas. Studies have shown that the northward spreading of the castor bean tick in Sweden and Russia appear to be associated with climate change, especially milder winters and extended growing seasons.
A report by the Natural Resources Defense Council predicts lyme disease could expand throughout the United States and northward into Canada, as temperatures warm, allowing ticks to move into new regions.
"Warmer temperatures, increases in rainfall, and milder winters can favor tick survival," noted Bobbi Pritt, director of clinical parasitology at the Mayo Clinic, in an email to Scientific American magazine.
Kuhn told VOA that as their range expands, the danger from ticks is growing.
"It’s better to be prepared now to begin to understand how we might be able to control them now, than when we have the outbreak of a new disease and everybody says 'Let's do something,' and we will not be prepared. We're preparing ahead of time," he said.
Reflecting on the last 10 years of research, Hill says that though her team has come to the end of genome mapping, they’re really just at the beginning of advancing work into understanding the biology of ticks.
"I don’t think we’ve appreciated the diversity of bacteria and viruses that ticks can transmit and we’re just at the very beginning of getting a better appreciation of that and understanding that ability to transmit pathogens," she said.
As sequencing software technology catches up, they hope to sequence many more tick species genomes at a much quicker pace.